Bone conduction hearing aid



Dec. l, 1936-. l E. c. N|CHQL|DES 2,062,372

BONE CONDUCTION HEARING AID Fiied Aug. 11, 1933 l 2 sheets-sheet 1 11 t YC. Ncolliaes` s Mmmm@ ATTORNEY l, 1936; E, Q NlCHQUDE 2,062,372

BONE CQNDUGTION HEARING AD FiledvAug.- 11, 1935 2 Sheets--Shee"tI `2 @wwf' @wz-59.

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INVENTOR S MALHMU ATTORNEY Patented Dec. l, 1936 A i i I d UNITED sTATEs PATENT-OFFICE 2,062,372 l BONE CONDUCTION HEARING AID Emmanuel Christ Nicholides, New York, N. Y.. assigner, by mesne assignments, to Sonotone Corporation, New York, N. Y., a. corporation o!y New York Application August 11, 193s, serial No. 684,712`

This invention relates to bone-conduction hearhearing-inducing vibratory energy required forl ing-aids andV it has among its objects an imimparting hearing by bone conduction." proved inertia-reaction bone-conduction receiver A bone-conduction receiver of my invention as of small size suitable for inconspicuous wear by actually built and used is shown in Figs. 1 to 7.

the user and able to impart hearing-inducing It is made in the form of a small vcompletely- 5 mechanical vibrations to the sound-conducting closed casing I and is shown in Fig. 1 held against bone structure of a hard of hearing person for the rnastoid bone by means of a head band inducing sound in his hearing center. clamped over the head. Sound-frequency oscil- The features and objects of the invention will latory currents may be supplied to the receiver be best understood from the following descripfrom any suitable source, such as a Aportable set, 10 tion of exemplications thereof, reference being comprising a ltransmitter microphone 2 conhad to the accompanyingdrawings, Whereinnected througha cutout switch in series with a Fig. 1 is a view of the head of a person carrying batteryr 3 and a microphone amplifier 4 and cord a bone-conduction receiver exemplifying the in. 5 to terminal plugs 6 leading into the casing I. vention, the associated elements of the hearing- 'I'he transmitter microphone, the'microphone am- 15 aid being shown diagrammatically; plier and all the other elements of the circuit Fig. 2 is a vertical sectional view of the reare small and may be easily hidden in the clothceiver along line 2--2 of Fig. 3; ing of the user. Sound waves acting upon the Fig. 3 is a horizontal sectional view of the rediaphragm of the transmitter 2 induce corre- 0 ceiver along line 3-3 of Fig. 2; sponding currents in the amplifier 4 and the Fig. 4 is a vertical sectional view of the receiver amplied speech currents are impressed through along line 4 4 of Fig. 3; cord 5 on the mechanism within the receiver Fig. 5 is a horizontal sectional view through casing I. the receiver along line 5 5 of Fig. 2; The construction of the receiver is shown in Fig. 6 is an elevational view of the base wall detailin Figs. 2 to '7. It comprises av small casof the receiver casing, the inner part of it being ing having a base 1 and an elongated cover 8 shown in section; tting against the edges of the base and attached Fig. '7 is a top view of the receiver as Worn on thereto by means of screws 9, and terminal block the head; II rising above the base. Figs. 8, 9, 10 and 11` are views similar to Figs. To permit easy coupling of the receiver surface 30 2, 3, ,4 and 5, respectively, of a modiiied form of against the bone structure I2, the casing I is the receiver; adjustably mounted on a bracket I3 embracingl Figs. 12 and 13 are side elevational and top the upper Sides 0f the Casing cover and having views partially in section of modifications of the inward pivot projectionsV I4 ttinginto suitable receiver shown in-Figs. 2 to 5, and 8 to 11, recooperating depressions I5 in the cover walls to spectively'; and support the casing and press its exposed base Figs. 14 and 15 show an elevational rear view Surface intO CIOSe engagement With the bone, and a side elevational, partially-sectional view of structure I2. This pressure is supplied by the modifications of receivers of the type shown in head band I6 which is clamped over the head, 40 Figs. 2 to 5, and 8 to 11', respectively. its lower end being secured to the upper cross 40 According to the invention, the casing of an piece of the' bracket I3 and exerting the pressure inertia-reaction,bone-conduction receiver utiliz- Supplied by lthe head bandthroughrhe bracket ing a floating vibrator unit for imparting heararms I3' and the pivots I4 on the casing base. ing-inducing inertia-reaction forces to a casing and therethrOugh On'the bone Structure.

Wall is provided with a. curv-ed external coupling Inside the easing iS mOunied an'electro- 45 surface for securing a good impedance match magnetic Vibrator mit 24 Comprising a magnetic between thegenclosed vibratory structure and the l(Sore Structure 25 and a diaphragm 26 The magbone structure 0f the user against which the netic core structure comprises an elongated percoupling surface is pressed. Large inertia-reacmamut-magnet plate 21 Carrying WO L-Shaped tion forces are developed within the receivercas- SOfi ireh D018 pieces 23 having inwardly Project- 50 ing by utilizing 'an electromagnetic vibrating ing arms 29 ehdirlgin Dole faCeS 30 forming Small structure having setV screws enabling accurate gapS'3 With the adjacent surface of the diaxing of the critical magnetic gap distance of the Dhragm Strip 25 The Outwardly extending pole enclosed vibrating unit essential for producing piece arms are rmly attached over soft iron with the small receiver the great amount of spacers 32 to the adjacent ends of core plate 21 55 spaced from the core by the gaps extending from theinner edges of the spacers 32.

To permit accurate fixing of the small critical pole gaps 3l of the order of about to y of a thousandth of an inch between the pole faces I0 and the diaphragm strip 28, set screws` 21 are screwed in through the magnet core plate 21 into threaded holes in the oyerlying arm portion of the two'pole pieces 28. By turning the set screws 21.

the pole faces 20 may be moved to increase or decrease the gap 30 in front cf the pole faces. In assembling the magnetic core structure 2l. its upwardly projecting pole pieces 28 are made to terminate at the same level as the fiat surfaces of the supporting blocks 32 that are to hold the ends of the diaphragm. After completely assembling the core structure, the Aupper surface of the pole pieces and the blocks 32 are ground to the same level. The coils Il are then mounted in place and the at diaphragm is secured by itsscrews 35 to the ends of the blocks 34. Thereupon the adjusting screws 31 are turned until the pole pieces are brought to a position wherein they do not freeze and are fit for operation.

Although the gap'is made about V3 to 3; of a mil long, satisfactory results may also be obtained with somewhat larger'- gaps.

Two inducing coils M mounted on the pole pieces 29 are connected to contact lugs 46 riveted at their lower ends to terminal bushings 21 fastened in the terminal block 20 at the bottom end of the base for engaging the plugs 6 of the supply cords` 5. l

The diaphragm 26 has an enlarged center portion lying above the pole faces 30 and its ends are rigidly clamped by screws 35 to the flat upper lsurfaces of the non-magnetic spacer blocks 34.

The center portion 5i of the diaphragm bridges the space between the pole faces 30 of the Acore and provides-a .path for the flux between the two core pole faces 30 through the gaps 8i, connected in series. The end portions of the diaphragm are narrower than the center portion 5i and merge into center portion 5I by gradually Widening intermediate portions.

The rigidity, thickness and shape of the diaphragm 20 arechosen to give it a stiffness necessary to prevent freezing between the diaphragm and the core pole faces. Its stiffness is chosen to prevent freezing of the diaphragm at a gap of about '1/3 to 1/2 mil and its resonance is at about 1,000 cycles per second. In the vibrator shown in Figs. 2 to 7, the diaphragm is made of cold rolled steel and has a thickness of 15 mils. The operating gap between the diaphragm and the .core is about 1/2 mil. vBy making its end portions narrow and the center portion 5l gradually wider, the end portions have the smallest stiifness, the stiffness gradually increasing in the regions near the center portion where it reaches its greatest value. flections of the center portion of the diaphragm and enables using of a thinner diaphragm. The gradual increase of the stiifness also prevents formation of vibration' nodes on the diaphragm.

Asshown in Figs. 4 to 6, the vibrator composed of the relatively heavy core structure 25 and the relatively light diaphragm 28 is mounted and supported as a unit on the inner center portion of the casing base 1, by attaching the center portion of the diaphragm to an anchor member` 55 This limits the maximum derigidly imbedded in the body of the base 1. The anchor member BB is of metalf like brass, and has a large plate-shaped rear portion BB imbedded conical depressions B1, I8 imbedded within the rigid mold body of synthetic resin material. The anchor member 55 is provided with an inwardly protruding, short anchor block li to which the lateral ends of center portion Il of the diaphragm are rigidly secured by screws I0 threaded into holes 6|.

When completely assembled the casing base 1 carries on its anchor member 5B the center piece 5I of the diaphragm 26. The two projecting narrow extensions of the diaphragm 26 carry, in turn, on the blocks vM the completely assembled rigid core structure including the core members 21, 28 and coils 4l, so that the entire vibrator structure is carried by the anchor |55 at the center of the casing base 1 of the casing. The spacing between the vibrator structure and the adjacent walls is sufficient to permit free vibration thereof on the anchor i5 towards and away from the base. Since the vibration amplitude is small, very little clearance is needed. By making the vibrator structure elongated and symmetrical with respect to the point of its anchoring point on the base, the vibratory forces are symmetrically imparted to the base and uniformly distributed thereover, securing a good coupling between the base 1 and the bone structure underlying it. A satisfactory impedance match between the vibration of the vibrator unit in the casing and the mass of base 1 and the bone structure is thus obtained.

In the bone-conduction vibrator as actually constructed and in use, the dimensions and weights of the principal elements are as follows: The permanent magnet bar is of tungsten steel, has a length of 1.125, a width of .475, and a thickness of .093 inches; the pole pieces are of soft iron steel, have a thickness of .050, and a total length of .600 inch. The diaphragm is of cold rolled steel, half hard temper, and has a length of 1.125, a maximum width of the 'center of .590, and of the'end portions of .275 inch, and a thickness of .015 inch; the center portion has a length of .175 inch at the outer edge, and a length of '.375

inch at the 'junction with the narrow middlev extensions. The total eiective vibratory mass of the diaphragm unit, including the diaphragm and the base attached thereto, is 7.8 grams; and the Astiffness of the diaphragm is about 8X10s dynes per centimeter. 'Ihe gaps have an equal length of about 1/2 mil when the armature diaphragm is under the action of the permanent magnetic field. The assembled vibrator mechanism with the casing has a length of 1%. a width of H, and, a height of 1/2 inches. The total weight of the complete vibrator with the casing is about 20 grams.

The bone-conduction receiver described above will, notwithstanding its small size and small weight, transmit into the bone structure of the head of a person of impaired hearing more vibratory power than required for giving satisfactory hearing. Transmission of the large amounts vof power is obtained by the provision of a minute critical gap spacing between the diaphragm and the core pole faces of the order of 1A; mil, and by the use of a diaphragm proportioned to permit vibrations withan/amplitude of about 1/2 mil while preventing gap freezing. Balanced transfer of the vibrations and prevention of distortions on the diaphragm is secured by the symmetric support of the vibratory mass at the Junction of the central portion of the diaphragm tothe central portion of the base.

Only the centralnodal portion of the vibrator mechanism is utilized for coupling the vibrator mechanism to the bone structure.' and substantially the entire mass of the vibrator mechanism is carried in a floating condition and utilized to produce the inertiareaction forces required for transmitting hearing-inducing vibratory energy to the bone structure of the user.

In Figs. 8 to 1l I have shown a modified form of the bone-conduction receiver of my invention. It comprises a casing |03 having a base |04 and an elongated cover |05 fitting the base having a' contact surface |06 held against the bone structure |01. l

To an anchor member rigidly imbedded within the base Vis secured the center portion l| of a diaphragm ||2 having 'extensions ||3 clamped to the core.

The core structure ||4 comprises an elongated rigid permanent magnet bar ||5 magnetized to have one pole, for instance, a north pole ||6 in' the center, and two south poles ||1 at its ends.

A soft iron center core is secured by a threaded end portion |2| in a threaded hole |22 within the center of the permanent magnet bar I |5 making the opposite end of the projecting core portion |20 the negative pole of the magnet core.'

The flat south-pole ends of -the permanent magnet bar ||5 are secured to soft iron core blocks by riveting extensions |26v of these blocks into holes within the bar ends.

The permanent magnet bar ||5 with the two soft iron blocks |25 and the center core member |20 constitute an E-shaped magnetic core structure having a center core with a pole face |28 of one polarity, and two end cores |25 with pole faces of opposite polarity.

The threaded mounting of the supported end of the center core within the hole of the magnetic bar ||5 enables accurate adjustment and maintenance of an accurate minute gap of the order of about 1/2 mil between the center portionv of the diaphragm lying over the center core pole face.

The core portion lying above the threaded end is wider than the threaded portion and a lockv washer |30 is placed between it and the inner wall of the bar H 5 to lock the core |20 in position.

An inducing coil |32 is connected through flexiblewires |34 to connecting lugs |35 attached to bushings |36 mounted within the terminal block |30.

Ihe unit of Figs. 8 to 11 is thus freely suspended within the casing and. is free to vibrate within the casing on its anchor coupling with the base.

As in the vibrator of Figs. 2 to 4, it will develop a great vibratory power while imparting to the bone structure large vibratory forces o f small displacement and maintaining its operating gap in` enabling uniform and large transfer of the power into the bone structure.

By matching the amplitudes of the vibrations impressed by the vibrator with the characteristics of the bone structure, the energy transfer to the bone structure is greatly increased. Such improved operation is obtained by increasing the coupling area between the contact member of the receiver and the bone structure engaged thereby.

An embodiment of a bone-conduction kreceiver arranged to operate with an increased contact surface with large forces and small vibration amplitudes is shown in Figs. 12 and 13. The vibrator casing and vibrator mechanism in its interior may be made as in the structures shown in Figs. 8 to 11, and 2 to5. To secure better coupling of the vibration transmitting member with the bone structure, I shape the contact surface of the base 5| of the vibrator unit to conform to the shape of the bone structure. Such large contact surface can be easily provided on the outer contact surface of the base by shaping in accordance with a cast of the bone portion which it is to match. From collections of casts of the bone structures of groups of similar persons, average contact surfaces can be shaped that may be used to advantage bydiierent persons having similar bone structures.

A bone-conduction receiver |60 having a large area vibration transfer contact surface and avoiding the necessity of making bases with different contact surfaces is shown in Figs. 14 and 15. It has a contact face |6|`shaped to fit in general outline the shape of the bone structure on a predetermined portion of the skull, and has on the contact face several contact areas |62 slightly -projecting above the contact face so as to grip the bone structure from several angles, with the in dividual contact areas shaped to engage a large area of the bone portion struc-ture against-which it rests. These projecting contact areas may have either slightly convex or slightly concave flexure so as to give in their average actions an effect of a large surface.

The bone-conduction receivers described above are inconspicuous in size, light in weight, and able to deliver more than suicient vibratory power to induce by bone conduction satisfactory sound in the inner ear of the user. 'I'heir electromagnetic vibrator mechanism is an independentv self-sustaining unit. It combines a large-mass magnetic core with a small-mass magnetic diaphragm into a symmetric low-reluctance magnetic-path structure with the core and diaphragm vibrating relatively to each other across one or more very small gaps of opposite polarity having a length of the order of about 1/3 to 1/2 mil at a diaphragm stiffness of a magnitude which will positively prevent gap freezing at resonance, without exceeding the freezing stiffness by more than twice. A nodal portion of the diaphragm is used as the sole support of the vibrator mechanisml and has the vibrations of the unit impressed thereon. A nodal diavphragm portion is rigidly coupled to and supported on a contact member having a large concave surface engaging and pressing against a sound conducting bone structure to secure a good match of the impedance of the vibrator. unit with the mass of the bone structure and a large transfer of vibratory power.

The principles underlying the invention and the various features thereof may be utilized. in conjunction'with hearing-aid devices in. many other'- ways that will suggest themselves to those skilled in the art, and itis accordingly desired that the exposing said sections to the action of electric sound-frequency oscillations producing a vibratory motion between said sections. and coupling means for coupling one vibratory section to soundinducing bonestructure outside the ear canal of the user, said coupled vibratory section constituting a casing carrying said other vibratory structure in a floating condition within said casing, said floating vibrator section having sufficient inertia for exerting hearing-inducing reaction forces on a wall of said casing, said wall having a concave external coupling surface shaped to impart under the action of said reaction forces convergent hearing inducing forces to spaced portions of said bone structure.

2. In a portable bone-conduction hearing-aid device, a bone conduction receiver, suitable for inconspicuous wear by a deafened, having two relatively movable vibratory sections, means for exposing said sections to the action of electric sound-frequency oscillations producing a vibratory motion between said sections, and coupling means for coupling one vibratory section to soundinducing bone structure outside the ear canal of the user, said coupled vibratory section constituting a casing carrying said other vibratory structure in a floating condition within said casing, said floating vibrator section having suicient inertia for exerting hearing-inducing reaction forces on a wall of said casing, said wall having a coupling surface larger than the overlying cross sectional area of said casing shaped to impart under the action of said reaction forces hearing inducing forces to spaced portions of said bone structure.

3. In a portable hearing-inducing device, a bone conduction receiver, suitable for inconspicuous wear by a deafened, having two relatively movable magnetic core members constituting a low reluctance flux path spacedby a small gap of the Order of one mill, windings interlinked with said path for producing by sound-frequency current oscillations a vibratory motion between said core members, and coupling means for couplingone f core member to sound-inducing bone structure outside the ear canal of the user, said coupled core member constituting a part of a casing carrying the other core member in a floating vibratory condition inside said casing, said floating core member having sumcient inertia for exerting hearinginducing reaction forces on a wall of said casing, said wall having an external concave coupling surface shaped to impart under the action of said reaction forces convergent hearing inducing forces to spaced portions of said bone structure.

4. In a wearable hearing aid device. anelectromagnetic bone conduction receiver of inconspicuous size comprising a driven member, a driving member of substantial mass resiliently joined to said driven member to constitute therewith a vi bratory structure of fixed dimensions forming a low reluctance magnetic flux path including a gap of the order of a fraction of a thousandth of an inch separating opposing pole faces of said members, said driven member ccnstituting s. part Aof a casing enclosing and resiliently carrying said driving member in a floating condition inside said casing, means for couplingv by external pressure an exterior wall of said casing to hearing inducing bone structure of the user, windings interiinked with said flux path producing under. energization by, audio-frequency current oscillations corresponding magnetic forces across said gap for im.- parting through the inertia reaction of said fioating driving member hearing inducing vibratory energy to said bone structure and set screw means extending through two spaced facing portions of the enclosed vibratory structure for fixing the structural relation of the floating part of the vibratory structure relatively to the driven-,member and maintaining the dimensions o`f the gap at a fixed value at which the amplitude of! the vibrations of' said members is ofthe order of the gap distance while preventing, freezing of the pole faces across said gap.

'5. In a wearable hearing aid device, an electromagnetic bone conduction receiver of inconspicuous size comprising a driven member, a driving member including a rigid permanentk magnet bar of substantial mass resiliently joined to said driven member to constitute therewith a vibratory structure of fixed dimensions forming a low reluctance magnetic flux path including a gap of the order of a. fraction of a thousandth of an inch separating opposing polefaces of said members, said driven member constituting a part of a casing enclosing and resiliently carrying said driving member in a floating condition inside said casing, means for coupling by external pressure an exterior wall of said casing to hearing inducing bone structure of the user, windings interlinked with said flux path producing under energization by audio-frequency current oscillations corresponding magnetic forces across said gap for imparting through the inertia reaction of said floating driving nember hearing inducing vibratory energy to said bone structure, and set screw means extending through said rigid magnet bar and engaging another spaced facing portion of the enclosed vibratory structure for fixing the structural relation of the floating part of the vibratory structure relatively to the driven member and maintaining the dimensions of the gap at a fixed value at which the amplitude of the vibrations of said members is of the order of the gap distance while preventing freezing of thepole faces across said gap.

6. In a wearable hearing aid device, an electromagnetic vibrating device of inconspicuous size suitable for wear by the user comprising a'driven member, a driving member of substantial mass resiliently joined to said driven member to constitute therewith a vibratory structure of fixed dimensions forming a low reluctance magnetic flux path including a gap of critical length separating opposing pole faces of said members, a casing enclosing said members, one of said members being secured to an interior wall of said casing and resiliently carrying the other member in a floating condition inside 'said casing, windings interlinked with said flux path producing under energization by audio-frequency current oscillations corresponding magnetic forces across said gap for imparting a vibratory motion to the floating member inside said casing, and set screw means extending through one of said members and engaging another facing portion of the enclosed vibratory structure for fixing the structural relation of the floating member relatively to the member extending from said casing and maintaining the gap distance between the opposite pole faces within fixed limits while preventingfreezing of the pole faces during the vibrations of said floating member.

'7. In a wearable hearing aid device, an electromagnetic bone conduction receiver of inconspicuous size comprising a driven member, a driving member of substantial mass resiliently joined to said driven member to constitute therewith a vibratory structure of fixed dimensions forming a low reluctance magnetic flux path includinga gap of the order yof a fraction of a thousandth of an inch separating opposing pole faces of said members, said driven member constituting a part of a casing enclosing and resiliently carrying said driving member in a iioating condition inside said casing, means for coupling by external pressure an exterior wall of said casing to hearing inducing bone structure of the user, windings interlinkedY with said flux path producing under energization by audio-frequency current oscillations corresponding magnetic forces across said gap for im' parting through the inertia reaction of said floating driving member hearing inducing vibratory energy to said bone structure, and set screw means extending through a portion of said oating vibratory structure and engaging another facing portion o! the enclosed vibratory structure for fixing the structural relation o! the oating part of the vibratory structure' relatively to the driven member and maintaining thedimensions of the gap at a fined value at which the amplitude of the vibrations of said member is of the order of the'gap distance while preventing yfreezing vof the pole faces across said gap.

' C. NICHOLIDES. 

